Method of manufacturing sheath for electric accumulator plates



United States Patent "ice 3,216,864 METHOD OF MANUFACTURING SHEATH FOR ELECTRIC ACCUMULATOR PLATES Charles James Bushrod, Cheadle, and Clifford James Hall,

Bolton, England, assignors to Chloride Batteries Limited, Lancashire, England, a British company No Drawing. Filed Apr. 10, 1962, Ser. No. 186,332 Claims priority, application Great Britain, Apr. 19, 1961, 14,160/ 61 2 Claims. (Cl. 136-148) This invention relates to lead-acid electric accumulators and more particularly to tubular type plates therefor. In such plates lead conducting spines extend between top and bottom bars of the plate and the active material around each spine is enclosed within a perforated or porous tube.

For many years it was the practice to employ slitted ebonite tubes for enclosing the active material, while more recently fabric sheaths consisting of a plurality of interconnected tubes or pockets woven, knitted or braided from various acid-resisting synthetic yarns have been used or proposed in order to improve performance and/ or lower the cost of production.

Among the objects of the present invention are the provision of fabric tubes for tubular type plates as aforesaid of a type of material much less expensive than those used heretofore, and whose permeability to the electrolyte and ability to retain the active material is also still further improved. Further objects are to provide such tubing in the form of an interconnected multi-tube or pocketed sheath arrangement which has greater strength in resisting the expansive forces which occur in the positive active material during discharge, and which which is in itself possessive of lateral stabilty and sufficient longitudinal stiffness or rigidity to enable conventional manufacturing techniques, involving vigorous shaking, to be used for filling the tubes with active material and compacting same.

A still further object of the invention is to provide a method of manufacturing such fabric sheaths which involves the use of simpler techniques than those used heretofore and which lowers still further the cost of production thereof.

According to the present invention there is provided a fabric sheath for a tubular type plate of a lead-acid electric accumulator, in the form of a plurality of permeable individual tubes or pockets interconnected by web portions extending between adjacent tubes, in which the walls of the individual tubes consist of non-woven felt like fabric made from fibres of an acid-resisting thermoplastic resin.

Preferably both the tubes or pockets and the web portions are formed originally from non-woven felt like fabric. The interconnecting web portions may each consist of a strip of the said non-woven fabric which has been fused to become non-fibrous and homogeneous, or they may each comprise a strip consisting of a solid matrix of an acid-resisting thermoplastic resin with the non-woven fabric embedded therein, the web portions in either case imparting both longitudinal stiffness and lateral stability to the sheath.

The use of a non-woven fabric affords a number of advantages and improvements over the woven types of fabrics used and suggested heretofore. The fabric itself is less costly and yet mechanically is strong. Furthermore non-woven fabrics of the felted type may be produced which retain the active material in an assembled plate more effectively than does a woven fabric, while at the same time allowing freer circulation therethrough of the acid electrolyte of an accumulator. Thus the interstices between the fibres of a felted fabric may be 3,216,864 Patented Nov. 9, 1965 sufficiently large to render the fabric highly permeable to the electrolyte, yet by virtue of their labyrinthine nature the fabric will still afford maximum retention of the active material.

Preferably the sheath comprises two layers of the said non-woven fabric joined together along spaced parallel strips in order to produce the said tubes or pockets and the interconnecting web portions.

In accordance with a further feature of the invention, there is provided a method of manufacturing a fabric sheath as described above which includes the steps of superimposing, one on the other, two layers of a nonwoven fabric made from fibres of an acid-resisting thermoplastic resin, and joining the two layers together by welding along spaced parallel strips to provide the plurality of individual tubes or pockets interconnected by web portions.

The welding may be effected so as to unite the two layers at the said web portions by transforming the layers of non-woven fabric at each web portion into a fused integral whole which is non-fibrous and homogeneous. Alternatively the two layers may have been previously impregnated with the said second thermoplastic resin, the welding then being effected so as to form at each web portion a solid matrix consisting of the second thermoplastic resin with the layers of non-woven fabric imbedded therein.

Preferably the said two layers of fabric are joined together over the web portions by radio frequency welding, and they may be corrugated prior to being welded together. Each layer may be set in such corrugated form by heat treatment between suitably shaped dies so that when the two layers are welded together along the said parallel strips the resulting pockets are of true cylindrical form. Alternatively, the two layers may be welded together along the said parallel strips without pre-corrugation, cylindrical rods then being inserted as formers into the resulting pocketed sheath and the form of the sheath being set by similar heat treatment.

The homogeneous or solid web portions effectively resist any tendency to tear apart during the expansion of the positive active material which occurs when the accumulator discharges. Furthermore the said web portions, which are in effect solid strips of plastic material, render the sheath dimensionally stable, and in particular prevent any tendency to bulge or bow outwardly in a lateral direction during the initial electrochemical formation of the active material and prior to the formed plate being assembled in the accumulator container. The web portions also assist in imparting longitudinal stiffness to the sheath so that the well known conventional methods of filling the pockets with active material and compacting same, as used with rigid ebonite tubes and involving vigorous shaking, can be employed.

Alternatively when. using pre-corrugated and pre-set layers of non-woven fabric as described above, the troughlike portions of the two layers may be filled or pasted with the active material and the conducting spines laid in position prior to the two layers being placed together and welded over the web portions. By this means the operation of filling the pockets in a completed sheath is avoided altogether.

The non-woven fabric may consist of fibres of any suitable acid-resisting thermoplastic resin yarn, including polyvinylchloride and thermoplastic copolymers thereof, polyethylene, polypropylene and polyacrylic resins.

Fibres of such resins may be welded or fused together at temperatures below those at which decomposition occurs, and fabrics formed from such fibres may also be given a permanent form or set by heat treatment.

Some synthetic resin yarns, for example of polyester resins, although thermoplastic have melting points so high that very great care needs to be exercised in carrying out the welding operation if an undesirable degree of decomposition is to be avoided. Non-Woven fabrics made from fibres of such resins, for example a polyester resin of terephthalic acid and ethylene glycol, may still be used conveniently by pre-impregnation of the fabric with a solution of a different thermoplastic resin, for example polyvinyl chloride or polystyrene. The impregnant then provides substance for the welds which can be made at temperatures below the decomposition temperature of the polyester fibres. The resulting weld comprises a matrix consisting of the impregnant with the polyester fibres embedded therein. Similarly, the impregnant can be cured by heat treatment at temperatures well below the decomposition temperature of the polyester fibres, whereby a permanent form or set is given to the polyester fabric.

Alternatively, non-woven fabrics made from fibres of such polyester resins may be joined at the web portions by the use of suitable cementing resins or by stitching. In order to impart a set to the tubes of the pocketed sheath it is again preferable to impregnate the fabric with a suitable resin which can be subsequently cured.

What is claimed is:

1. A method of manufacturing a fabric sheath for a tubular type plate of a lead acid accumulator in the form of a plurality of permeable individual tubes interconnected by web portions extending between adjacent tubes, in which the walls of the individual tubes consist of nonwoven felt-like fabric made from fibres of an acid-resisting thermoplastic resin which comprises:

setting each of two layers of non-woven fabric in a corrugated form by heating the same between suitably shaped dies, thereby imparting a permanent set to the fibres of the fabric;

superimposing the two corrugated layers one on the other;

and joining said superimposed layers together by welding along opposed parallel strips thereof and thereby forming said web portions and said tubes, whereby each intermediate web portion consists of non-woven fabric which has been fused to become solid, nonfibrous and homogeneous.

2. A method of manufacturing a fabric sheath for a tubular type plate of a lead acid accumulator in the form of a plurality of permeable individual tubes interconnected by web portions extending between adjacent tubes, in which the walls of the individual tubes consist of non-woven felt-like fabric made from fibres of an acidresisting thermoplastic resin which comprises:

impregnating a layer of polyester non-woven fabric with an acid-resisting thermoplastic resin;

setting each of the two layers so impregnated in a corrugated form by heating the same between suitably shaped dies, thereby curing the thermoplastic resin and imparting a permanent set to the corrugated form of the fabric;

superimposing the two corrugated layers one on the other;

and joining said superimposed layers together by welding along opposed parallel strips thereof, defining a plurality of web portions intermediate of a plurality of tubular portions, whereby each intermediate web portion comprises a solid matrix consisting of the said thermoplastic resin with the layers of polyester non-woven fabric embedded therein.

References Cited by the Examiner UNITED STATES PATENTS 1,243,371 10/17 Willard 136-147 2,297,248 9/42 Rudolph 136-146 2,511,887 6/50 Vinal 136-146 2,569,169 9/51 Heritage 136-146 2,591,755 4/52 Wilson et al. 136-146 2,972,000 2/61 Boriolo 136-43 FOREIGN PATENTS 229,327 5/59 Australia.

WINSTON A. DOUGLAS, Primary Examiner.

JOHN H. MACK, Examiner. 

1. A METHOD OF MANUFACTURING A FABRIC SHEATH FOR A TUBULAR TYPE PLATE OF A LEAD ACID ACCMULATOR IN THE FORM OF A PLURALITY OF PERMEABLE INDIVIDUAL TUBES INTERCONNECTED BE WEB PORTIONS EXTENDING BETWEEN ADJACENT TUBES, IN WHICH THE WALLS OF THE INDIVIDUAL TUBES CONSIST OF NONWOVEN FELT-LIKE FABRIC MADE FROM FIBRES OF AN ACID-RESISTING THERMOPLASTIC RESIN WHICH COMPRISES: SETTING EACH OF TWO LAYERS OF NON-WOVEN FABRIC IN A CORRUGATED FORM BY HEATING THE SAME BETWEEN SUITABLY SHAPED DIES, THEREBY IMPARTING A PERMANENT SET TO THE FIBRES OF THE FABRIC; SUPERIMPOSING THE TWO CORRUGATED LAYERS ONE ON THE OTHER; AND JOINING SAID SUPERIMPOSED LAYERS TOGETHER BY WELDING ALONG OPPOSED PARALLEL STRIPS THEREOF AND THEREBY FORMING SAID WEB PORITONS AND SAID TUBES, WHEREBY EACH INTERMEDIATE WEB PORTION CONSISTS OF NON-WOVEN FABRIC WHICH HAS BEN FUSED TO BECOME SOLID, NONFIBROUS AND HOMOGENEOUS. 